The thought may not have occurred to football lovers all over the world who watched transfixed on Sunday evening as Real Madrid and Barcelona served up a thrilling Clásico, but it is possible that the best team in Spain were not playing.

As Andrés Iniesta scored the first of seven goals at the Bernabéu, the Atlético Madrid express was departing Seville, taking the players, coaching staff and fans home after their 2-0 win at Real Betis.

The players followed the Clásico on the radio and via Twitter, working within the limits of mobile phone reception. With an hour left of their journey, news filtered through of Lionel Messi’s winning penalty, meaning Atlético stayed top of the league, with nine games left.

The carriage carrying the team erupted, with the exception of the ever-cautious coach Diego Simeone, who stayed calm, loyal to his mantra of only ever thinking about the next game.

In the 27 months Simeone has been in charge of Atlético, the club have won the Europa League, the European Super Cup and the Copa del Rey. But only one member of the squad has won the league title wearing red and white stripes: Simeone himself.

The Argentine scored the opening goal of Atlético’s 2-0 win over Albacete on the final day of the 1995-96 season which delivered their first title in 19 years. If his team can win all nine of their remaining games, he will get his hands on the trophy again, 18 years later.

From the touchline, Simeone, previously best known to English football as the man who got David Beckham sent off at the 1998 World Cup, lives the emotions of his team’s games with the same energy he used to boss the team’s midfield, contesting every refereeing decision, celebrating every goal scored, cursing every goal conceded. He even pumps his fist when the opposition miss.

In the press room he is much calmer, considered, repeating his mantra of going “game-by-game”. In other words, he can be a bit dull. And those are his words.

“I’m sorry, I’m boring,” he said when asked for his thoughts on the Clásico. “We’ve got a match before then which is more important to us. If you think I said ‘game-by-game’ a lot before, I’m going to say it even more now.”

The victory over Betis was a hard-fought win that characterised Atlético’s season. Betis are bottom of the league but made things difficult for Atlético until they were reduced to 10 men in the second half. With an extra man, Atlético captain Gabi broke the deadlock with a thumping shot from outside the area, soon followed by Diego Costa’s 30th goal of the season. Midfielder Gabi explained after the match: “It was a very important win, but we had to work hard, we had to suffer.”

Suffering is part of Atlético Madrid’s DNA, coming with the territory of sharing a city with the most successful team in Europe. The word even made its way into the club’s centenary anthem: “What a way to suffer, what a way to die, what a way to win, what a way to live.”

Atlético have always known how to suffer, but now they know how to win too. Their 22 victories have taken them to the top of the league, level on points with Real Madrid but above their neighbours due to their superior head-to-head record, and one point above Barcelona.

A few of those wins, such as the 7-0 hammering of Getafe or the 5-0 mauling of Betis earlier in the season, have spoken of a team who can compete with Barcelona and Real Madrid, despite the disparity in their budgets. Real and Barca have €500 million (£418 million) to work with, Atlético get by on €100 million (£83.5 million). As Simeone has put it: “There’s a small difference between us, about €400 million.”

In other games, such as away to Betis, Celta Vigo and Elche, all teams near the bottom of the league, they also won, but they had to sweat for the points, showing signs they are not in the same category as Spain’s big two. Simeone explained: “It took Barcelona 15 minutes to beat Elche, we needed 78.”

While the big two have the money, Atlético have the spirit. “The secret is the union of the dressing room, the fact we are all playing for the same cause,” says Gabi.

It is that spirit, the ability to keep defying the odds, which gives Atlético reason to believe they can win the league. Next up is a straight forward home game with Granada, followed by a daunting trip to Athletic Bilbao, who have only lost once at home in the league this season.

But Atlético should not be too concerned: they became the first team to win at Bilbao’s new stadium in January when they knocked the Basques out of the Copa del Rey. There are three further fixtures that will concern Atlético: a trip to fierce rivals Valencia, the home game with Villarreal and then the daunting prospect of facing Barcelona at the Nou Camp on the final day of the season.

Atlético may have the weakest squad of the three title candidates and the hardest run in, but with every win, confidence grows. Even Simeone is starting to drop hints that he also believes, remarking after the win at Betis: “We have the peace of mind to do whatever we have to do.”

Four players who have helped Atlético reach the top

Thibaut Courtois The Chelsea loanee has let in only 19 goals all season, providing a solid shield at the back which assures the defence, and regularly producing outstanding saves when called upon.

Diego Costa The rampant striker’s 23 league goals have ensured few people at the Calderón miss Radamel Falcao anymore, and his unpredictable movement has made the team a nightmare to defend against.

Koke The Manchester United target’s 11 assists make him the second top provider of goals this season in La Liga, and he is quick to tuck in from the wing to chip in with defensive duties when necessary.

Miranda Alongside Diego Godin, the Brazilian has helped make Atléti the meanest defence in the league – he is as comfortable defending with his back against the wall as he is bringing the ball forward.